Those who have irregular blood glucose concentration levels are medically required to regularly self-monitor their blood glucose concentration level. An irregular blood glucose level can be brought on by a variety of reasons including illness such as diabetes. The purpose of monitoring the blood glucose concentration level is to determine the blood glucose concentration level and then to take corrective action, based upon whether the level is too high or too low, to bring the level back within a normal range. The failure to take corrective action can have serious implications. When blood glucose levels drop too low—a condition known as hypoglycemia—a person can become nervous, shaky, and confused. That person's judgment may become impaired and that person may eventually pass out. A person can also become very ill if their blood glucose level becomes too high—a condition known as hyperglycemia. Both conditions, hypoglycemia and hyperglycemia, are potentially life-threatening emergencies.
Common methods for monitoring a person's blood glucose level are invasive in nature. Typically, in order to check the blood glucose level, a drop of blood is obtained from the fingertip using a lancing device. The blood drop is produced on the fingertip and the blood is harvested using the test sensor. The test sensor, which is inserted into a testing unit, is brought into contact with the blood drop. The test sensor draws the blood to the inside of the test unit which then determines the concentration of glucose in the blood.
One problem associated with this type of analysis is that there is a certain amount of pain associated with the lancing of a finger tip. Diabetics must regularly self-test themselves several times per day. Each test requires a separate lancing, each of which involves an instance of pain for the user. Further, each lancing creates a laceration in the users skin which take time to heal and are susceptible to infection just like any other wound.
Other techniques for analyzing a person's blood glucose level are noninvasive in nature. Commonly, such techniques interpret the spectral information associated with light that has been transmitted through or reflected from a person's skin. An advantage of this type of noninvasive analysis is that there is no associated pain or laceration of the skin. However, thus far, such techniques have proven unreliable because many techniques fail to recognize the many issues which impact the analysis. For example, many noninvasive reflectance and transmission based systems do not account for the fact the obtained spectral data contain glucose information from the portion of body tissue being analyzed as a whole, and is not limited to blood glucose. Other techniques do not account for irregularities in the spectral signal of the analyte due to instrumental drift, temperature changes in the tissue under analysis, spectral characteristics of the tissue that change due to pressure changes, etc. that can occur during the analysis or between analysis. These irregularities can impact the quality of the calibration model or the algorithms that used to determine the analyte concentrations from the non-invasively collected spectral data. The spectral data that has these irregularities can not be used by the algorithms to determine the analyte concentrations.
Accordingly, there exists a need for a reliable noninvasive system for the determination of analytes in body fluids.